1. Field
A condensing type clothes dryer having a heat pump cycle, and a method for controlling a condensing type clothes dryer having a heat pump cycle are disclosed herein.
2. Background
Generally, a clothes dryer is an apparatus for drying laundry by evaporating moisture contained in the laundry, by blowing a hot blast generated by a heater into a drum. The clothes dryer may be classified into an exhausting type clothes dryer and a condensing type clothes dryer according to a processing method of humid air having passed through a drum after drying laundry.
In the exhausting type clothes dryer, humid air having passed through a drum is exhausted outside of the clothes dryer. On the other hand, in the condensing type clothes dryer, humid air having passed through a drum is circulated without being exhausted outside of the clothes dryer. Then, the humid air is cooled to a temperature less than a dew-point temperature by a condenser, so moisture included in the humid air is condensed.
In the condensing type clothes dryer, condensate water condensed by a condenser is heated by a heater, and then heated air is introduced into a drum. While humid air is cooled to be condensed, thermal energy of air is lost. In order to heat the air to a temperature high enough to dry laundry, an additional heater is required.
In the exhausting type clothes dryer, air of high temperature and high humidity should be exhausted outside of the clothes dryer, and external air of room temperature should be introduced to be heated to a required temperature by a heater. As drying processes are executed, air discharged from an outlet of the drum has low humidity. The air is not used to dry laundry, but rather, is exhausted outside of the clothes dryer. As a result, a heat quantity of the air is lost. This may degrade thermal efficiency.
Recently, a clothes dryer having a heat pump cycle, capable of enhancing energy efficiency by collecting energy discharged from a drum and by heating air introduced into the drum using the energy, has been developed.
FIG. 1 is a schematic view of a related art condensing type clothes dryer having a heat pump cycle. Referring to FIG. 1, the condensing type clothes dryer may include a drum 1 into which laundry may be introduced, a circulation duct 2 that provides a passage such that air circulates via the drum 1, a circulation fan 3 configured to move circulating air along the circulation duct 2, and a heat pump cycle 4 having an evaporator 5 and a condenser 6 serially installed at or along the circulation duct 2 such that air circulating along the circulation duct 2 passes through the evaporator 5 and the condenser 6. The heat pump cycle 4 may include a circulation pipe that may form the circulation passage such that a refrigerant circulates via the evaporator 5 and the condenser 6, and a compressor 7 and an expansion valve 8 installed at or along the circulation pipe between the evaporator 5 and the condenser 6.
In the heat pump cycle 4, thermal energy of air having passed through the drum 1 may be transferred to a refrigerant via the evaporator 5, and then the thermal energy of the refrigerant may be transferred to air introduced into the drum 1 via the condenser 6. With such a configuration, a hot blast may be generated using thermal energy discarded by the conventional exhausting type clothes dryer or lost in the conventional condensing type clothes dryer.
FIG. 2 is a schematic view illustrating a flow of air passing through the evaporator 5 and the condenser 6, in a related art condensing type clothes dryer to which the heat pump cycle 4 has been applied. Referring to FIG. 2, air discharged from the drum 1 may pass through the evaporator 5 and the condenser 6 sequentially, along the circulation duct 2. The circulation duct 2 and the evaporator 5 (or the condenser 6) may be formed to have no gap therebetween, such that a largest amount of air passes through the evaporator 5 and the condenser 6. Such a configuration is advantageous in that a drying time and an the amount of energy used may be reduced, as heat exchange efficiency is enhanced as a speed of air passing through the evaporator 5 and the condenser 6 and a heat transfer coefficient are increased.
However, such a structure where there is no gap between the circulation duct 2 and a heat exchanger (including the evaporator 5 and the condenser 6) may have the following problems. Generally, as a temperature of the outlet of the drum 1 is increased during a drying process, an evaporation pressure of a refrigerant evaporated by the evaporator 5, and a condensation pressure of a refrigerant condensed by the condenser 6 are increased. Further, in a case in which an amount of a drying load is large or an amount of water contained in an object to be dried is large, a condensation pressure may be increased to a value more than a reliable pressure of the compressor 7 as a drying process is executed. As a result, a condensation temperature of the condenser 6 and a discharge temperature of the compressor 7 are increased, which may cause many problems. Accordingly, the condensation temperature of the condenser 6 and the discharge temperature of the compressor 7 are controlled to be lower than a predetermined value.
More specifically, the following methods may be performed. For example, an inverter compressor may be formed to have its rpm changeable. Thus, if a condensation pressure of a condenser is increased, an rpm of the inverter compressor may be controlled to be lower than a reference condensation pressure. However, in the inverter compressor, as a DC power is used as a driving power source, a driver for converting an AC power into a DC power and converting a current frequency into a required frequency should be installed. This may increase fabrication costs.
FIG. 3 is a view illustrating that a secondary condenser and a cooling fan may be added to a heat pump cycle applied to a related art condensing type clothes dryer. A secondary condenser 26 and a cooling fan 23 may be mounted adjacent to a primary condenser 16 of the heat pump cycle 4. When a temperature of the primary condenser 16 is increased to a value greater than a predetermined temperature, the secondary condenser 26 and the cooling fan 23 cool the primary condenser 16 using air which is outside of the clothes dryer, and radiate additional thermal energy inside of the heat pump cycle. In this case, an installation cost of the secondary condenser 26 and the cooling fan 23 may increase fabrication costs.
FIG. 4 is a graph illustrating pressure-time relation when a constant speed type compressor is turned on/off. In a related art method for controlling a constant speed type compressor, as shown in FIG. 4, when a condensation pressure of a condenser reaches a reference value, the compressor may be temporarily stopped. Then, the compressor may be restarted such that the condensation pressure is maintained at a level less than the reference value. However, as the compressor may be stopped and restarted repeatedly, a drying time may be increased. This may cause energy for driving the circulation fan and the drum to be wasted.